Artificial Dielectric Medium Research Articles

Use of the Sub Array From Microstrip Elements in Dielectric Layers Before the Aperture of Phased Antenna Array for Impedance Matching at Scanning

The solution of an electrodynamics’ problem of radiation of the Phased antenna array (PAR), representing the infinite periodic structure generated from the open ends of waveguides is offered. Before an aerial aperture sub array from strip (tape) elements in the dielectric layers is installed. The array in the dielectric layers f organizes of strip-geometry elements artificial medium. The problem is reduced to system of the integrated equations of 1-st sort which is decided concerning unknown fields in the aperture of the open ends of waveguides and currents on stripe-geometry elements. In a wide frequency band the numerical analysis of radiation parameters artificial dielectric medium on PAR electrodynamics’ characteristics at beam steering.

Artificial dielectric beam-scanning prism for the terahertz region

We design and fabricate an artificial dielectric prism that can steer a terahertz beam in space and experimentally investigate its behavior. The artificial dielectric medium consists of a uniformly spaced stack of metal plates, electromagnetically equivalent to an array of parallel-plate waveguides operating in tandem. At an operating frequency of 0.3 THz, we observe a maximum beam deflection of 29°, limited by the precision of the available spacers. Spring-loading the spacers between the plates allow us to scan the beam continuously and dynamically over a range of 5°. The measured beam intensity maps at the input and output of the device reveal very good Gaussian beam quality and an estimated power efficiency of 71%. As a possible real-world application, we integrate the prism into the path of a free-space terahertz communication link and demonstrate unimpaired performance.

A Luneburg Lens for the Terahertz Region

We experimentally demonstrate a two-dimensional Luneburg lens for the THz region using a waveguide-based artificial-dielectric medium. The substrate material of the lens is Teflon with the top and bottom surfaces coated with silver to form a quasi-parallel-plate waveguide. The top surface of the device has a curved conical profile and the bottom surface is flat. The lens can focus an approximately 2-cm diameter input beam at a frequency of 0.162 THz to a spot size of 3.4 mm (less than 2λ) at the diametrically opposite edge of the device.

Tunable superconducting Josephson dielectric metamaterial

We demonstrate a low-dissipation dielectric metamaterial with tunable properties based on the Josephson effect. Superconducting wires loaded with regularly spaced Josephson junctions (critical current Ic ≈ 0.25 μA) spanning a K-band waveguide and aligned with the microwave electric fields create a superconducting dielectric metamaterial. Applied dc current tunes the cutoff frequency and effective permittivity of this unique electric metamaterial. The results are in agreement with an analytical model for microwave transmission through the artificial dielectric medium.

Artificial dielectric polarizing-beamsplitter and isolator for the terahertz region

We demonstrate a simple and effective strategy for implementing a polarizing beamsplitter for the terahertz spectral region, based on an artificial dielectric medium that is scalable to a range of desired frequencies. The artificial dielectric medium consists of a uniformly spaced stack of metal plates, which is electromagnetically equivalent to a stacked array of parallel-plate waveguides. The operation of the device relies on both the lowest-order, transverse-electric and transverse-magnetic modes of the parallel-plate waveguide. This is in contrast to previous work that relied solely on the transverse-electric mode. The fabricated polarizing beamsplitter exhibits extinction ratios as high as 42 dB along with insertion losses as low as 0.18 dB. Building on the same idea, we also demonstrate an isolator with non-reciprocal transmission, providing high isolation and low insertion loss at a select design frequency. The performance of our isolator far exceeds that of other experimentally demonstrated terahertz isolators, and indeed, even rivals that of commercially available isolators for optical wavelengths. Because these waveguide-based artificial dielectrics are low loss, inexpensive, and easy to fabricate, this approach offers a promising new route for polarization control of free-space terahertz beams.

Terahertz Artificial Dielectric Lens.

We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2 cm diameter beam to a spot size of 4 mm, at the design frequency of 0.17 THz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices.

Enhancement of Tilted Beam in Elevation Plane for Planar End-Fire Antennas Using Artificial Dielectric Medium

This communication describes a simple and effective beam-tilting technique for planar end-fire antennas using an artificial dielectric layer. The proposed approach is based on the phase differential resulting from a high refractive-index medium that is achieved using double G-shaped resonators (DGRs) in a ${5} \times {4}$ array. The array is oriented normal to the direction of the main beam emanating from the antenna. To demonstrate the principle, the technique is applied to a bow-tie antenna, which is designed at the WiMAX frequency band (3.4–3.6 GHz). The antenna performance was verified practically, and the measured results confirm that the direction of antenna’s maximum beam can be refracted by 35° in the H-plane, which is larger than conventional techniques. In addition, a maximum gain enhancement of 5 dB is achieved when the beam is tilted. Reflection-coefficient of the proposed structure is maintained better than $- {10}\;\text{dB}$ across its operational band.

A 2-D Artificial Dielectric With <formula formulatype="inline"> <tex Notation="TeX">${0 \leq n < 1}$</tex></formula> for the Terahertz Region

We demonstrate a 2-D artificial dielectric medium suitable for the terahertz region by exploiting the characteristic frequency dependence in the phase velocity of the lowest order transverse-electric (TE1) mode of the parallel-plate waveguide (PPWG). This artificial medium exhibits a plasma-like behavior having a frequency-dependent refractive index that varies between zero and unity. Using this medium, we demonstrate the optical phenomena of total internal reflection and Brewster's effect, and also demonstrate a convergent PPWG-lens.

Electromagnetic models of the lightning return stroke

Lightning return‐stroke models are needed for specifying the source in studying the production of transient optical emission (elves) in the lower ionosphere, the energetic radiation from lightning, and characterization of the Earth's electromagnetic environment, as well as studying lightning interaction with various objects and systems. Reviewed here are models based on Maxwell's equations and referred to as electromagnetic models. These models are relatively new and most rigorous of all models suitable for computing lightning electromagnetic fields. Maxwell's equations are numerically solved to yield the distribution of current along the lightning channel. Different numerical techniques, including the method of moments (MoM) and the finite difference time domain (FDTD) method, are employed. In order to achieve a desirable current‐wave propagation speed (lower than the speed of light in air), the channel‐representing wire is embedded in a dielectric (other than air) or loaded by additional distributed series inductance. Capacitive loading has been also suggested. The artificial dielectric medium is used only for finding the distribution of current along the lightning channel, after which the channel is allowed to radiate in air. Resistive loading is used to control current attenuation with height. In contrast with distributed circuit and so‐called engineering models, electromagnetic return‐stroke models allow a self‐consistent full‐wave solution for both lightning‐current distribution and resultant electromagnetic fields. In this review, we discuss advantages and disadvantages of four return‐stroke channel representations: a perfectly conducting/resistive wire in air, a wire embedded in a dielectric (other than air), a wire in air loaded by additional distributed series inductance, and a wire in air having additional distributed shunt capacitance. Further, we describe and compare different methods of excitation used in electromagnetic return‐stroke models: closing a charged vertical wire at its bottom with a specified grounded circuit, a delta‐gap electric field source, and a lumped current source. Finally, we review and compare representative numerical techniques used in electromagnetic modeling of the lightning return stroke: MoMs in the time and frequency domains and the FDTD method. We additionally consider the so‐called hybrid model of the lightning return stroke that employs a combination of electromagnetic and circuit theories and compare this model to electromagnetic models.

Artificial dielectric medium possessing simultaneously negative permittivity and magnetic permeability

An artificial dielectric medium comprising two sublattices of spherical particles made of a high-dielectric-constant (high-e) material, which are embedded into a low-e dielectric matrix, are considered. Particles belonging to different sublattices have different diameters. It is shown that the properties of this composite structure are equivalent to those of an isotropic medium possessing a negative refractive index (n 200 can be made of a ferroelectric material.

Electrostatic image theory for the dielectric sphere

The image of a point charge in a conducting sphere, produced by Kelvin's inversion theory, has become well known since its formulation in 1848. The corresponding theory in terms of point charges does not exist for the dielectric sphere. In the present paper, electrostatic image theory for the dielectric sphere, both for the field outside and inside of the sphere, is developed. Simple analytic expressions in terms of a point charge and a line charge are seen to arise in both cases. The theory is extended to give simple images for dipole and line sources. Possible application of the new expressions in simplified quasi‐static analyses of interactions of dielectric spherical particles in artificial dielectric media is pointed out.

Electrostatic image theory for layered dielectric sphere

Static image theory for a homogeneous dielectric sphere, recently formulated by one of the authors, is generalised to the problem of a multilayer dielectric sphere in terms of a line-image charge. The imageline source is seen in this case to be in relation to the so-called static reflection coefficient that could be labelled as a finite Mellin transformation. This transformation is discussed and a Table of corresponding transforming functions is given. The result can be applied in a more complete quasistatic analysis of interactions of layered dielectric spherical particles in an artificial dielectric media. More closely, a two-layer sphere is considered with special cases of a thin layer, and that of a low contrast between the layers. Numerical results are calculated for the radiowave propagation problem of attenuation due to melting hail particles, assumed to be composed of a spherical ice core with a spherical water shell.

Leaky-wave antennas using artificial dielectrics at millimeter wave frequencies

A novel approach for the design of leaky-wave antennas using artificial dielectrics at millimeter wave frequencies is discussed. The general radiation characteristics of leaky-wave structures of finite length are presented. The feasibility of frequency scanning and dielectric scanning (changing the direction of the beam by varying the relative permittivity of the electrically controlled liquid artificial dielectric medium) of a leaky-wave antenna using rodded artificial dielectric is investigated theoretically. Calculations shown that the beam angle changes from 20° to 50° off broadside when the frequency is changed from 31.1 to 35.4 GHz or the permittivity of the embedding medium of the artificial dielectric is changed from 1.6 to 2.04. Over a scan range of about 40° the beamwidth is almost constant. For large scan range, the beamwidth of a dielectric-scanned antenna (DSA) is about 15 percent less than the frequency-scanned antenna (FSA). The gain of a DSA is greater than the FSA and also has less variation over the scan range. The power efficiency is approximately the same for both the antenna types with worst case efficiency being about 85 percent.

Artificial-Dielectric Electronically Scannable Antenna

This paper describes the radiation characteristics of a cylindrical leaky-wave antenna, which is electronically scannable, and made of artificial-dielectric medium. The latter consists of thin parallel, perforated, conducting plates, embedded in a dielectric of relative-permittivity, ∈r. The parallel-plate artificial-dielectric antenna because of its cylindrical, compact form, and ease of fabrication, is preferable to the parallel-wire artificial-dielectric antenna reported earlier. Radiation patterns with ring-source, and waveguide excitation, for both TE-, and TM-modes are found to have in most cases, a single narrow beam whose magnitude and position can be adjusted by suitable choice of artificial-dielectric parameters, antenna diameter and frequency.

Electrically Controllable Liquid Artificial Dielectric Media

New work is reported on electric field controlled liquid dielectrics demonstrating their application in control devices at 35 and 95 GHz. Liquid artificial dielectric design approaches and performance prediction are also discussed, with emphasis on electronic beam steering of millimeter-wave antennas. References are included listing much of the prior work done in this area.

A leaky-wave antenna using an artificial dielectric medium

A narrow-beam antenna using an artificial dielectric medium with effective permittivity less than unity has been investigated theoretically and experimentally. Complex propagation constant for a wave propagating along the structure is evaluated by solving the dispersion relation. The analysis indicates the presence of a leaky-wave mode. The radiation pattern is calculated by using Kirchhoff-Huygens integration method. Experimental results for an antenna of this type designed for operation at X band are reported and compared with theoretical calculations. Beam position varies from 17\deg to 47\deg when the frequency is changed from 8.6 to 11.5 GHz. Over this frequency range the half-power beamwidth varies from 5.6\deg to 4.8\deg . An expression for the half-power beamwidth of a leakywave antenna of finite length has been derived and discussed in the Appendix.

Narrow-beam antennas using an artificial dielectric medium with permittivity less than unity

Radiation from a line source of electric current placed inside a slab of artificial dielectric medium with a permittivity less than unity has been studied. It is found that radiation patterns with single or multiple narrow beams may be obtained by the proper choice of parameters. In a typical case for er=0.1378, µr=1.322, a beamwidth of about 1° is obtained when the thickness of artificial dielectric slab is about 2.33 times the wavelength.

Erratum: Narrow-beam antennas using an artificial dielectric medium with permittivity less than unity

Radiation from a line source of electric current placed inside a slab of artificial dielectric medium with a permittivity less than unity has been studied. It is found that radiation patterns with single or multiple narrow beams may be obtained by the proper choice of parameters. In a typical case for er=0.1378, µr=1.322, a beamwidth of about 1° is obtained when the thickness of artificial dielectric slab is about 2.33 times the wavelength.

Birefringent Filter for Millimeter Waves

A scale model (f/sub 0/ =20 GH/sub z/ of a Solc-type birefringent wave filter for millimeter wavelengths is described. The filter consists of five cascaded identical half-wave plates, or crystals, each composed of an artificial anisotropic dielectric medium with its reference axis tilted at some prescribed angle to the plane of the input polarization. The design and analysis of an individual plate, using Collin's second-order theory of the birefringence of artificial anisotropic dielectrics, and the analysis of multielement filters (filters composed of many plates), aided by Evans' matrix method, are discussed. The experimental filter was tested in the range of 18 to 33 GHz, and its measured performance was found to compare well with the theoretical performance over a major portion of the range of frequencies used in the tests. A synthesis procedure for optimum (equal-ripple stopband) response multielement filters is given, together with tables of plate angles for such filters. In this procedure, the Dolph approximation and the Harris synthesis are combined.

Thickness Corrections for Capacitive Obstacles and Strip Conductors

Capacitive thickness corrections are derived exactly for two basic geometries involving pairs of semi-infinite plates. In one arrangement the pair of plates are coplanar, while in the other they are parallel to each other. In each case the total capacitance per unit length between the pair of plates is infinite, but the incremental increase of capacitance when the thickness is increased from zero to a value t is finite. These capacitance increments are evaluated, and it is shown how they may be used as approximate thickness corrections in a great varity of more complicated geometries involving capacitive obstacles in waveguide, coaxial line, and artificial dielectric media. They may also be applied to coupled-strip-line conductors. As examples, the corrections are applied in detail to a waveguide iris, and to three useful coupled-strip-line cross sections.